Carina's Pillars of Destruction: the view from ALMA (1910.09164v1)

Abstract: Forming high-mass stars have a significant effect on their natal environment. Their feedback pathways, including winds, outflows, and ionising radiation, shape the evolution of their surroundings which impacts the formation of the next generation of stars. They create or reveal dense pillars of gas and dust towards the edges of the cavities they clear. They are modelled in feedback simulations, and the sizes and shapes of the pillars produced are consistent with those observed. However, these models predict measurably different kinematics which provides testable discriminants. Here we present the first ALMA Compact Array (ACA) survey of 13 pillars in Carina, observed in $^{12}$CO, $^{13}$CO and C$^{18}$O J=2-1, and the 230 GHz continuum. The pillars in this survey were chosen to cover a wide range in properties relating to the amount and direction of incident radiation, proximity to nearby irradiating clusters and cloud rims, and whether they are detached from the cloud. With these data, we are able to discriminate between models. We generally find pillar velocity dispersions of $<$ 1 km s$^{-1}$ and that the outer few layers of molecular emission in these pillars show no significant offsets from each other, suggesting little bulk internal motions within the pillars. There are instances where the pillars are offset in velocity from their parental cloud rim, and some with no offset, hinting at a stochastic development of these motions.

• The paper details ALMA CO isotopologue observations to measure pillar kinematics, revealing velocity dispersions below 1 km/s.
• The paper finds that pillar masses, ranging from tens to hundreds of solar masses, support ongoing star formation with dense cores exceeding 10^21 cm⁻².
• The paper validates theoretical models by linking observed low-turbulence, diverse pillar morphologies to the impact of high-mass star feedback.

Insights from the ALMA Observations of Carina’s Pillars

This paper presents a detailed paper of the stellar feedback processes in the star-forming region of the Carina Nebula using the ALMA Compact Array (ACA) enhanced with Total Power (TP) data. By observing the J=2-1 transitions of CO and its isotopologues in 13 distinct pillar structures, the authors explore the influence of high-mass star formation on their surrounding environments. The quantitative analysis provides a more nuanced understanding of these pillars' kinematic and dynamic conditions, which are pivotal in testing and refining theoretical models of stellar formation and feedback.

Observational Methodology

Utilizing ALMA's high sensitivity to CO isotopologues ($^{12}$CO, $^{13}$CO, and C$^{18}$O) at 230 GHz, the paper achieves insight into both the optical depth of CO emission and internal structures of the pillars at sub-arcsecond resolution. This ensures high fidelity in detecting gas column densities and reveals intricate pillar dynamics, especially kinematic features indicative of stellar feedback.

Key Findings

1. Velocity Dispersions and Kinematics: The pillars exhibit velocity dispersions generally less than 1 km/s, a direct contrast with the expectation of significant internal motions from models emphasizing turbulence (e.g., those by \citet{Gritschneder09}). The minimal internal motions identified align more with the feedback dynamics proposed by \citet{Dale12II}, suggesting a Kolmogorov decay in initial turbulence with less dominant internal pillar motions.
2. Mass and Column Density Estimates: The investigation estimates pillar masses ranging from a few tens to several hundred solar masses, affirming a potential for ongoing star formation given the observed dense cores, particularly those that emit C$^{18}$O. Moreover, peak column densities reach thresholds supportive of star formation, exceeding $10^{21}$ cm$^{-2}$.
3. Feedback-induced Morphologies: Pillars display diverse morphologies and evolutionary stages influenced by incident radiation and proximity to ionizing sources, validating simulations where feedback sculpts the interstellar medium into observed structures.
4. Comparative Analysis with Theoretical Models: A crucial component of the paper is testing model predictions; the observed velocity gradients and pillar structures serve as empirical benchmarks. Findings generally favor models prescribing low-turbulence conditions, challenging models predictively relying on high internal dynamics.

Practical and Theoretical Implications

The insights acquired from kinematic data provide robust discriminants between different feedback models, pushing for more comprehensive understanding and calibration of simulations regarding feedback processes. Practically, they emphasize the necessity of multi-wavelength and high-resolution approaches (such as integrating ALMA with MUSE) in observational astrophysics to unravel the complex interplay of processes driving star formation. The approach provides a framework for anticipated future observations using upcoming facilities like JWST, further probing the lifecycle of molecular clouds and regions subjected to stellar feedback.

Future Directions

This work lays foundational groundwork for subsequent, more focused studies on star-forming regions. Future work could expand upon the temporal sequence of star formation in Carina by integrating ALMA data with longitudinal infrared and optical surveys. Additionally, further theoretical developments must accommodate these empirical constraints, particularly improving upon models that inadequately account for low pillar turbulence and ordered morphological features observed herein.

In conclusion, the paper substantiates ALMA’s pivotal role in dissecting the micro-environments within complex star-forming regions, bringing clarity to feedback processes and their role in galactic scale star formation, thereby informing both current and future astronomical research methodologies.